fix(workbench): suppress unconfigured demo alerts

The not_configured branch previously promoted mock task failures into critical alerts. Return an explicit empty alert source so the exception badge reflects only actionable backend state.

src/features/workbench/components/workbench-top-bar.tsx

@@ -142,7 +142,7 @@ export function WorkbenchTopBar({
           open={openMenu === "alerts"}
           onOpenChange={createMenuOpenChange("alerts")}
           alerts={alerts}
-          sourceLabel={alertDataSource === "mock" ? "工况演示回退" : "后端运行态"}
+          sourceLabel={getAlertSourceLabel(alertDataSource)}
           conditionFeedVisible={conditionFeedVisible}
           onSelectAlert={onSelectAlert}
           onToggleConditionFeed={onToggleConditionFeed}
@@ -239,7 +239,7 @@ export function WorkbenchTopBar({
             open={openMenu === "compact-alerts"}
             onOpenChange={createMenuOpenChange("compact-alerts")}
             alerts={alerts}
-            sourceLabel={alertDataSource === "mock" ? "工况演示回退" : "后端运行态"}
+            sourceLabel={getAlertSourceLabel(alertDataSource)}
             conditionFeedVisible={conditionFeedVisible}
             onSelectAlert={onSelectAlert}
             onToggleConditionFeed={onToggleConditionFeed}
@@ -261,6 +261,12 @@ export function WorkbenchTopBar({
   );
 }
 
+function getAlertSourceLabel(source: WorkbenchAlertDataSource) {
+  if (source === "backend") return "后端运行态";
+  if (source === "mock") return "工况演示回退";
+  return "未配置告警源";
+}
+
 function getAnalysisOriginLabel(origin: AnalysisArtifact["origin"]) {
   if (origin === "backend") return "后端分析运行";
   if (origin === "demo") return "演示成果";